2.2.4.1 Nanomaterial for Sensors2.2.4.1 Nanomaterial for Sensors

Science & Technology Objective(s):• To use the aligned nanotube array as sensor for

monitoring gas flow rate• To fabricate nano-size gas sensors using

semiconducting oxide nanobelts

Design principles:

2.2.4 Nanotechnology2.2.4 Nanotechnology

Z.L. Wang, Georgia Tech

Collaborations:• Government – NASA, Oak Ridge National Lab• URETI – Peter Heskerth

Proposed Approach:Sensor for gas flow rate:• Step 1: Synthesizing aligned nanotube arrays• Step 2: Building the set up for field emission

measurement under flowing gas environment• Step 3: Testing the device for engine applicationsOxide Nanobelt for Gas Sensors• Step 1: Synthesizing oxid nanobelts (ZnO)• Step 2: Build the electrodes using e-beam

lithography• Step 3: Testing the device for gas sensorNASA Relevance/Impact:• In-situ real time monitoring of gas flow at a very

confined region for providing better control on engine working condition

• In-situ, real time monitoring of residual gas at high temperature with high selectivity

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Vgas

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CarnonNanotubes

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Gold electrodes (50 nm thick)

ZnO nano-ribbon

(w=285nm,h=110nm)

SiO2 (~120n thick)

2.2.4.1 Nanomaterials for Sensors First Year M1 M2 M3 M4 M5 M6

TASKS

1 Synthesis of aligned carbon nanotubes

2 Synthesis of oxide nanobelts

M7 M8 M9 M10 M11 M12

3 Building set-up for field emssion testing

4 Build devices using the oxide nanobelts

2.2.4.1 Proposed Approach: Synthesis of Nanotubes2.2.4.1 Proposed Approach: Synthesis of Nanotubes

Furnace

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To pump

CH4

- Deposit Fe/Ni catalyst particles onto a ceramic substrate;

- Grown carbon nanotubes by decomposition of CH4 at high temperature;

- Control temperature and gas flow rate to optimize the alignment.

Z.L. Wang, Georgia Tech

- Emission current is a measure of the distance between the tips of the carbon nanotubes and counter electrode;

- The emission current drops if the nanotubes are bent by flowing gas;

- Monitoring the emission current can quantitatively determine the gas flow rate.

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CarnonNanotubes

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I0

2.2.4.1 Proposed Approach- Testing the Sensor2.2.4.1 Proposed Approach- Testing the SensorZ.L. Wang, Georgia Tech

Furnace

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Viewwindow Oxide powders alumina substrate

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Thermal coupleAlumina tube

Ar

2.2.4.1 Proposed Approach- Synthesis of Oxide Nanobelts2.2.4.1 Proposed Approach- Synthesis of Oxide Nanobelts

- Place oxide powder as the source material in the crucible;

- Thermal vaporization of the oxide followed by a deposition at the low temperature region results in the growth of nanobelts;

- Control temperature and gas flow rate to optimize the morphology.

Z.L. Wang, Georgia Tech

Two-probe measurements of electric conductance of a single nanowire under different temperature and gas partial pressure.

Nanowire

Insulator substrate

ElectrodeElectrode

2.2.4.1 Proposed Approach- Building Gas Sensors2.2.4.1 Proposed Approach- Building Gas Sensors

- The electric conductance of the nanobelt depends on the type and amount of molecules adsorbed on its surface

- Using the semiconductive oxide nanobelts, nanosensors using individual nanobelt will be built.

Z.L. Wang, Georgia Tech